AMMONIA, Harcrsnowx, or the volatile alkali, was one of the few substances known to the chemistry of the ancients; being referred to by Pliny under the name of vehement odor, which he evolved by mixing lime with nitrum (probably sal ammoniac). It derives its name A. from its being obtained front sal ammoniac, which was first procured by heating camels' dung in Libya, near the temple of .Jupiter Ammon. The atmosphere contains a minute quantity of A., amounting to 210-237 parts in 10,000,000.000 parts of air, which is equal to 1 volume of A. in 28,000,000 of air. it is likewise present in rain water in variable proportion. The supply of A. to the atmosphere is its evolution during the putrefaction of animal and vegetable substances, during the vinous fermentation, and the combustion of coal, It is likewise present in respired mr, and is therefore a product of the daily wear and tear of the animal system. The principal source of A. at the present time is the destructive distillation of coal, as in gas-makirg. The materials which pass over from the retort are partly uncondensable and truly gss_ious, and these are carried to our gas-jets and burned; but in other parts they are condensable, and are received during the purification of the gas, as a mixed tarry and watery liquid. On allowing this liquid to settle, the water portion, containing A., can be separated, and, hydrochloric acid being added to it, there is formed a compound of A. and hydrochloric acid, called chloride of ammonium, which can be obtained dry, by evaporating the solution down in shallow vessels. Pure A. is manufactured from this impure chloride of ammonium by mixing, it with its own weight of slaked lime in a retort, and applying a gentle heat, when the A. as 3 gas passes over, and is received in a vessel containing water. The solubility of A. in water is very great, 1 volume of water dissolving CO volumes of anunoniacal gas, increasing in bulk, and forming a liquid (liquor ammonia of the chemist, and hartshorn of the shops), which is lighter than water, its density being 8Th. The
solution of A. is transparent, colorless. and strongly alkaline. In taste it is acrid caustic, and in odor very pungent. Applied to the skin in a concentrated form, it blisters Exposed to the air, the A. escapes, and the solution thus gets weaker, and. reduced to-40° F,, it freezes. As generally obtained, even in the gaseous condition, it is in combination with the elements of one atom of water, and contains one of nitrogen. 4 hydrogen. and 1 oxygen Dry A. can be procured by passing the vapor of A., as ordinarily obtained, over fused chloride of calcium, when the water is abstracted, and true gaseous A. is left, having the composition 1 nitrogen, and 3 hydrogen Gaseous A. can be liquefied under pressure and cold, and then yields a colorless, clear, mobile liquid, with the characteristic odor and other properties of A. much intensified. A. combines with acids to form a class of salts which are of considerable importance. Thus, the crystallized sulphate of A. is very extensively used as a top-dressing by farmers, and is also mixed with manures where an increase of ammoniacal matter is desirable. The chloride of ammonium is also employed in agriculture; likewise largely by the Russian peasantry, as a condiment for flavoring food iu place of common salt.
In medicine, the gaseous A. has been rarely used. The solution of A. is employed as a means of rousing the respiratory and vascular systems; and of the speedy alleviation of spasm. It is also used as it local irritant and antacid. It is serviceable in dyspeptic complaints with preternatural acidity of stomach and flatulence; to produce local irritation or destruction of certain parts, and to render comparatively harmless the bites of poisonous animals, such as serpents and insects.